Why am I running out of fuel in the second city... My miners appear to be working?

The miners are probably only producing enough coal during the morning and evening shifts. At night there is no production so the coal storage depletes. Also the fire has two burning levels, one consumes more than the other but isn't always necessary. There are a few solutions.

1) Increase coal production (upgrading iron mine)

2) Reduce coal consumption (reducing workers in coal dependant factories - metal, mould, etc)

3) Reduce fire burning level